Without the Sahara desert, the Amazon rainforest wouldn't exist. Every year around 40m tonnes of dust is swept up from north Africa and whistled across the Atlantic Ocean, a distance of over 5,000km, before finally coming to rest in the Amazon basin in South America. This dust is the main source of minerals for the Amazon rainforest, fertilising the soil and keeping the rainforest healthy.

Around half of this dust cloud comes from just one place - the Bodélé depression in Chad. This sand filled pit lies in a bottleneck, between two mountain regions. To the north-west lies the Tibesti mountain range, and to the south-east lies the Ennedi massif. The structure of the mountains acts like a funnel, guiding and accelerating the surface winds over the Bodélé depression. During the winter these winds form a low level jet stream, flinging an average of 0.7m tonnes of dust every day towards the Amazon basin.

It is a hostile environment, but Pieter Vermeesch and Nick Drake, from the University of London, have discovered a comfortable way to view the dunes. Using monthly satellite images they have studied the way that the sand moves in the depression. Their work, published in the journal Geophysical Research Letters, confirms that the big crescent shaped sand dunes in the Bodélé depression are some of the world's speediest sand dunes. As a result nothing is permanent in the Bodélé - any house or road would be smothered in months.